Particularly in the plumbing and waterworks industries, situations frequently arise during installation or repair of piping where it is necessary to connect pipes to various fittings such as corporation valves, curb valves and various adapters. These situations can arise for example during water service line installation or repair. Such piping can include service tubes and may be made of polyvinylchloride (PVC) or galvanized steel for example.
Typically, such fittings are provided with a stub, usually externally threaded, for receiving a sealed fluid communicating connection with the pipe. The threading on such stubs are typically of an industry standard such as corporation fitting thread, to allow similarly-threaded couplings to be mounted thereon.
Such pipe-fitting couplings typically come in two main forms. In a first form the coupling is integral with the pipe. The present invention is directed to the second form wherein the coupling is a separate device which clamps on to, or is otherwise sealingly affixed to the end of the pipe. In either case the end of the coupling intended to engage the fitting stub is provided with internal threading and the coupling is connected to the fitting stub by turning one relative to the other thereby engaging the internal threading of the coupling with the external threading of the stub.
A typical manner in which such a separate coupling is used to connect a pipe to a fitting stub is as follows. First a coupling body, having internal threads at a forward end for engaging the external threads of the stub, and a constricted rearward end, is slid on to the pipe, rearward end first. A combination of various internal elements including seals and camming or gripping means are then slid on to the pipe. During this process it is imperative that each of the internal elements be placed on the pipe in the correct order and in the correct orientation. Failure to do so will typically result in failure of the connection. Finally, the coupling body is screwed onto the stub trapping and compressing the seals and the camming or gripping means. In particular, the constricted rearward end of the coupling body presses the seals and camming or gripping means against the end of the stub, or against the side of the pipe. The compressed seals create a hydrostatic seal between the stub and the pipe, while the camming or gripping means are urged to a locking and restraining position preventing the pipe from being pulled out of the coupling inadvertently. Using such a coupling, a secure pressure-sealed connection is made. An example of such a coupling for plumbing applications is described in U.S. Pat. No. 5,580,105 Miller Jr. et al. issued Dec. 3, 1996.
One difficulty with such couplings is the need for the user to handle a number of small elements (typically the internal elements) during installation. This can result in frustration on the part of the user while he fumbles with the various parts to ensure that they are installed in the correct order and orientation. As noted above, if the user fails to install these parts in the correct order and orientation, the connection can fail resulting in leakage. This disadvantage is particularly acute where installation takes place in difficult conditions, for example where the fitting is located in an awkward location, or where the installation is taking place on waterworks, often with the user standing in a wet and muddy hole where fingers are slippery and where a dropped part is irretrievably lost.
Another difficulty with such couplings is that the camming or gripping means are typically unitary circumferentially, or consist of a small number of wide grips spaced circumferentially. Thus if a unitary camming or gripping means fails, the coupling itself fails. Similarly, if one of a small number of grips fails, the strength of the coupling will be compromised. Further, with a unitary camming or gripping means or with wide grips, it is difficult to achieve positive attachment to pipes which are slightly out of round or which have an irregular outer surface (as is often the case with galvanized steel pipes).
Additionally, most present couplings are not reusable since the camming or gripping means used are permanently deformed during use.
Finally, with most present couplings the coupling can easily be under-tightened or over-tightened onto the pipe and/or the fitting, which may result in damage to the pipe, to the fitting, and/or to the coupling and may also result in failure of the coupling.